1. Field of the Invention
The present invention relates to an exhaust gas-purifying catalyst.
2. Description of the Related Art
Emission control on automobile, etc. is tightened in recent years. In order to respond to this, developed are exhaust gas-purifying catalysts that purify nitrogen oxides, etc. contained in the exhaust gas with a higher degree of efficiency. For example, Patent document 1 discloses an exhaust gas-purifying catalyst including a support containing cerium oxide and a precious metal supported by the support. Cerium oxide has a high oxygen storage capacity and is known as a component effective in improving the performance of the exhaust gas-purifying catalyst.
These exhaust gas-purifying catalysts, however, have a problem of easily emitting hydrogen sulfide (H2S), which is a cause of an offensive odor, during the process of purifying the exhaust gas. Thus, exhaust gas-purifying catalysts containing nickel (Ni) have been proposed as exhaust gas-purifying catalysts that reduce H2S emission (see Patent document 2, for example).
Ni is, however, designated as an environmental load substance in many countries and regions. For this reason, limitations on use of an exhaust gas-purifying catalyst containing a relatively large amount of Ni are becoming more widespread.